Create an YAML backend

[DAddYE]

Same of SQL, I think in some small scenarios would be great a builtin YAML or file store backend. So in that way we don't need to have external dependencies or any kind of persistence adapters.

[bkeepers]

I don't think I want to support this. I would encourage you to develop this as a stand-alone plugin. Should be pretty easy.

[bryckbost]

It's worth noting that if you do pursue a stand-alone plugin, you'll want to familiarize yourself with Psych and the differences between it and 1.8's Syck.